The continuous casting metallurgical method provides for casting the molten metal at a temperature of around 1500° C. in a bottomless mold. The shape of the ingot mold determines the section of the ingot which is extruded continuously.
A critical parameter of this method is the level of the molten metal in the ingot mold.
The monitoring of the molten metal level can be done conventionally by a suspended electromagnetic sensor as is shown, for example, by the document U.S. Pat. No. 4,647,854.
This type of sensor has two or three separate and independent coils which are all parallel to the molten metal surface. A first coil has an excitation function; the second and the third coil have a measurement function and are positioned on either side of the excitation coil.
The operating principle of this type of sensor consists in causing an alternating electrical signal to flow in the excitation coil, generated by control electronics, which creates a magnetic field.
This magnetic field is more or less disturbed depending on the level of molten metal present in the ingot mold.
Since the magnetic field varies according to the molten metal level, the voltage induced in the measurement coil which is adjacent to the molten metal is representative of the level of metal in the ingot mold.
The induced voltage which passes through the measurement coil adjacent to the molten metal is compared to the induced voltage which passes through the opposite, and therefore undisturbed, measurement coil, which makes it possible to deduce the liquid metal level from the difference between these two induced voltages.
In practice, the electromagnetic sensors are suspended above the molten metal, notably to avoid edge effects.
The positioning of these sensors above the molten metal considerably hampers interventions by the operators on the casting. These operators in fact have to constantly check the “cleanliness” of the surface of the molten metal and are required to intervene on the surface of the molten metal.
Furthermore, when changing the tube which feeds the molten metal into the ingot mold from a pocket situated upstream of the ingot mold, the sensor has to be purely and simply removed from the ingot mold.